SCHEDULED MAINTENANCE
Di-2-pyridyl ketone oxime [(py)2CNOH] in manganese carboxylate chemistry: mononuclear, dinuclear and tetranuclear complexes, and partial transformation of (py)2CNOH to the gem-diolate(2−) derivative of di-2-pyridyl ketone leading to the formation of NO3−†
Abstract
The use of di-2-pyridyl ketone oxime, (py)2CNOH, in manganese carboxylate chemistry has been investigated. Using a variety of synthetic routes complexes [Mn(O2CPh)2{(py)2CNOH}2]·0.25H2O (1·0.25H2O), Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Br2]·MeCN (2·MeCN), [Mn4(O2CPh)2{(py)2CO2}2{(py)2CNO}2Cl2]·2MeCN (3·2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2Br2]·2MeCN (4·2MeCN), [Mn4(O2CMe)2{(py)2CO2}2{(py)2CNO}2(NO3)2]·MeCN·H2O (5·MeCN·H2O) and [Mn2(O2CCF3)2(hfac)2{(py)2CNOH}2] (6) have been isolated in good yields. Remarkable features of the reactions are the in situ transformation of an amount of (py)2CNOH to yield the coordination dianion, (py)2CO22−, of the gem-diol derivative of di-2-pyridyl ketone in 2–5, the coordination of nitrate ligands in 5 although the starting materials are nitrate-free and the incorporation of CF3CO2− ligands in 6 which was prepared from Mn(hfac)2·3H2O (hfac− = hexafluoroacetylacetonate). Complexes 2–4 have completely analogous molecular structures. The centrosymmetric tetranuclear molecule contains two MnII and two MnIII six-coordinate ions held together by four µ-oxygen atoms from the two 3.2211 (py)2CO22− ligands to give the unprecedented [MnII(µ-OR)MnIII(µ-OR)2MnIII(µ-OR)MnII]6+ core consisting of a planar zig-zag array of the four metal ions. Peripheral ligation is provided by two 2.111 (py)2CNO−, two 2.11 PhCO2− and two terminal Br− ligands. The overall molecular structure of 5 is very similar to that of 2–4 except for the X− being chelating NO3−. A tentative reaction scheme was proposed that explains the observed oxime transformation and nitrate generation. The CF3CO2− ligand is one of the decomposition products of the hfac− ligand. The two MnII ions are bridged by two neutral (py)2CNOH ligands which adopt the 2.0111 coordination mode. A chelating hfac− ligand and a terminal CF3CO2− ion complete a distorted octahedral geometry at each metal ion. The CV of complex 3 reveals irreversible reduction and oxidation processes. Variable-temperature magnetic susceptibility studies in the 2–300 K range for the representative tetranuclear clusters 2 and 4 reveal weak antiferromagnetic exchange interactions, leading to non-magnetic ST = 0 ground states. Best-fit parameters obtained by means of the program CLUMAG and applying the appropriate Hamiltonian are JMn(II)⋯Mn((III) = −1.7 (2), −1.5 (4) cm−1 and JMn(III)⋯Mn(III) = −3.0 (2, 4) cm−1.
![Graphical abstract: Di-2-pyridyl ketone oxime [(py)2CNOH] in manganese carboxylate chemistry: mononuclear, dinuclear and tetranuclear complexes, and partial transformation of (py)2CNOH to the gem-diolate(2−) derivative of di-2-pyridyl ketone leading to the formation of NO3−](/en/Image/Get?imageInfo.ImageType=GA&imageInfo.ImageIdentifier.ManuscriptID=B412355G&imageInfo.ImageIdentifier.Year=2005)
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